The present invention relates to a variable displacement compressor for air-conditioning vehicles that compresses refrigerant gas and varies the displacement.
FIG. 8 shows an example of the variable displacement compressor (later simply called compressor). A crank chamber 102 is formed in a housing 101, in which a drive shaft 103 is supported. A lip seal 104 is located between the housing 101 and the drive shaft 103.
The drive shaft 103 is connected to a vehicle engine Eg through an electromagnetic clutch 105. The clutch 105 includes a rotor 106 coupled to the engine Eg, an armature 107 fixed to the drive shaft 103, and an electromagnetic coil 108. The coil 108, when excited, causes the armature 107 to be attracted to the rotor 106, which engages the armature 107 with the rotor 106. This transmits power from the engine Eg to the drive shaft 103. At this time, the clutch 105 is engaged. When the coil 108 is de-excited, the armature 107 is separated from the rotor 106, which disconnects power transmission from the engine Eg to the drive shaft 103. At this time, the clutch 105 is disengaged.
A lug plate 109 is fixed to the drive shaft 103 in the crank chamber 102. A swash plate 110 is coupled to the lug plate 109 through a hinge mechanism 111 and integrally rotates with the drive shaft 103. The inclination angle of the swash plate 110 relative to the axis L of the drive shaft 103 is varied. A snap ring 112 is secured to the drive shaft 103 to abut against the swash plate 110 and to limit its minimum inclination angle.
The housing 101 includes cylinder bores 113, a suction chamber 114, and a discharge chamber 115. A piston 116 is accommodated in each cylinder bore 113 to reciprocate. Each piston is coupled to the swash plate 110. A valve plate 117 is located in the housing 101. The valve plate 117 separates the adjacent cylinder bores 113 from the suction chamber 114 and from the discharge chamber 115.
Rotation of the drive shaft 103 is converted into reciprocation of each piston 116 through the lug plate 109, the hinge mechanism 111, and the swash plate 110. This draws refrigerant gas from the suction chamber 114 to the cylinder bores 113 through suction ports 117a and suction valves 117b of the valve plate 117. Refrigerant gas is compressed in each cylinder bore 113 and discharged to the discharge chamber 115 through discharge ports 117c and discharge valves 117d of the valve plate 117.
A spring 118 is located between the housing 101 and the drive shaft 103. The spring 118 urges the drive shaft 103 toward the front (left in FIG. 1) of the compressor along the axis L and absorbs dimensional tolerance of parts, which prevents chattering.
A bleed passage 119 connects the crank chamber 102 to the suction chamber 114. A pressurizing passage 120 connects the discharge chamber 115 to the crank chamber 102. A control valve 121 includes a solenoid and varies the opening size of the pressurizing passage 120. The control valve 121 operates depending on the passenger compartment temperature, a target temperature, disengagement of the clutch 105, the state of the engine Eg, and the like.
The control valve 121 varies the size of a valve opening to control the flow rate of gas in the pressurizing passage 120, which supplies high-pressure refrigerant gas to the crank chamber 102. The pressure in the crank chamber is varied by the relationship between the supply of refrigerant gas to the crank chamber 102 and the release of refrigerant gas from the crank chamber 102. This varies the difference between the pressure in the crank chamber 102 and the pressure in the cylinder bores 113, which varies the inclination of the swash plate 110. As a result, the stroke of the pistons 116 is varied, which adjusts the displacement.
When the clutch 105 is disengaged or when the engine Eg stops, the control valve 121 maximizes the size of the valve opening. This increases the pressure in the crank chamber 102 and the difference of the pressure in the crank chamber 102 and the pressures in the cylinder bores 113, which reduces the inclination of the swash plate 110. As a result, inclination of the swash plate 110 is minimized when the compressor is stopped. Therefore, the compressor is restarted with a minimum torque load, and less shock is produced.
However, in this prior art compressor, when the temperature in the passenger compartment is much higher than the target temperature, that is, when the cooling requirement is great, the control valve 121 closes the pressurizing passage 120 and maximizes the compressor displacement.
Suppose that the compressor operated is stopped by the disengagement of the clutch 105 or the shutting off of the engine Eg when operating at maximum development. Also, suppose that a controller minimizes the compressor displacement despite the cooling requirement to reduce the torque load on the engine Eg when the vehicle is suddenly accelerated.
In this case, the closed pressurizing passage 120 is suddenly opened to minimize the displacement. Accordingly, high-pressure refrigerant gas in the discharge chamber 115 is quickly supplied to the crank chamber 102, and the bleed passage 119 does not release the extra gas sufficiently, which increases the pressure in the crank chamber 102 excessively. As a result, the difference between the pressure in the cylinder bores 113 and the pressure in the crank chamber 102 is excessive.
Therefore, the swash plate 110 (shown by the broken line in FIG. 8) is forcefully abutted against the snap ring 112, which strongly draws the lug plate 109 rearward through the hinge mechanism 111. As a result, a strong rearward force is applied to the drive shaft 103, which moves the drive shaft 103 against the force of the spring 118.
When the drive shaft 103 moves rearward, the contact area between the lip seal 104 and the drive shaft 103 may shift. There may be foreign particles like sludge on the surface of the drive shaft 103 at the new contact area. Therefore, the sludge may enter between the lip seal 104 and the drive shaft 103, which degrades the performance of the lip seal 104 and causes gas leakage.
When the compressor is disengaged from the engine Eg and the drive shaft 103 moves rearward, the armature 107, which is fixed to the drive shaft 103, moves toward the rotor 106. The clearance between the rotor 106 and the armature 107 when the clutch 105 is disengaged is very small (0.5 mm, for example). The rearward movement of the drive shaft 103 eliminates the clearance between the rotor 106 and the armature 107, which causes the armature 107 to contact the rotating rotor 106. This causes noise and vibration and transmits power to the compressor.
The rearward movement of the drive shaft 103 during the acceleration of the vehicle moves the pistons 116 and the swash plate 110 rearward, which moves the top dead centers of the pistons 116 rearward. Accordingly, the pistons 116 collide against the valve plate 117 when the pistons 116 reach their top dead center positions. This causes noise, vibration, and damage to the pistons 116 and the valve plate 117.
To prevent the rearward movement of the drive shaft 103, it is possible to increase the force of the spring 118. However, this decreases the life of a thrust bearing 122, which receives the increased force, and increases power losses.